1. Field of the Invention
This invention relates to the pyrolytic production of a highly reflective solar control article by application of successive metal containing films to a glass substrate. In addition, these films provide a broad range of colors by reflection and transmission, optical uniformity and a durable surface coating.
2. Description of the Prior Art
Increasing use of flat glass as a structural material has emphasized the need to develop a means of controlling solar radiation while providing the color flexibility as required by architects. Solar control as a means of minimizing the cost of heating and cooling buildings is becoming increasingly critical due to energy and fuel shortages. Aesthetics dictate color flexibility.
Various methods have been attempted previously in an effort to develop these properties. Heat absorbing glasses wherein minor amounts of colorant oxides are added to the glass have been proposed. This method has not worked well for several reasons. Homogeneity and reproducibility are difficult and expensive to obtain. Heat absorbed by the glass is ultimately transferred to interior areas by reradiation, conduction, and/or convection. Thermal breakage, due to wide variations in temperature between the edges and the central portion of the glass panels, is encountered.
Attempts were made to produce a coated surface that would reflect the solar energy and thus limit the amount of absorption and the subsequent transmission to interior spaces. Deposition of films by electrolysis, vacuum sputtering, chemical reaction, and pyrolysis all suffered disadvantages. Electrolysis and vacuum sputtering are both difficult and relatively expensive. Sophisticated equipment is required and the size of glass that can be coated is limited by the physical size of the equipment. Except for small items such as optical lenses and the like, it is generally impractical and too expensive to produce such films. This is particularly true in connection with large glass sheets such as are used in producing vehicle or building closures.
Chemical deposition, like electrolysis and vacuum deposition, is also a comparatively expensive process requiring a number of time consuming and consequently expensive manipulations.
It had been generally difficult to obtain either adhesion or uniformity by pyrolytic methods of film application. However, the spray process offered by this method had the advantages of being very fast and extremely well adapted to high volume production where large square footages are encountered. Recent advances have been made in the pyrolytic application of metal and metal oxide films to yield adherent, uniform films.
Films of gold, platinum, and silver are known to yield high solar energy reflection. However, both the initial cost of materials and the cost of the best available method of deposition are prohibitive for large scale production of gold or platinum films. Pyrolytic methods have not been effective.
Silver is not quite as expensive and it has been successfully applied as a film by pyrolytic methods. In U.S. Pat. No. 3,528,845 Donley teaches a method to produce an optically uniform, adherent silver film that is both practical and economical. The silver film is pyrolytically deposited from a solution of a silver soap of an organic acid in an organic solvent with an amine being used as a solubilizing agent. The film produced exhibits excellent solar control properties.
Browne in U.S. Pat. No. 3,087,831 describes a pyrolytic method of applying a metal oxide film over a first layer of "loosely adhering silver powder". The silver powder imparts a hazy appearance rather than providing a high reflecting surface. This lack of optical uniformity tends to limit the solar control properties of the film. The metal oxide overcoat functions as a means of holding the silver powder in place as ooposed to a discreet property enhancing film.
A superior method of producing a metal oxide film was described by Mochel in U.S. Pat. No. 3,410,710. A solution of metal diketonate in an organic solvent is sprayed on a hot substrate to form a uniform metal oxide film. Because of its uniformity, the film provides relatively good control of solar energy. The control capabilities can be increased by applying multiple layers of metal oxide with intermediate layers of amorphous silica. However, optical quality diminishes and visible transmission decreases as a function of increasing thickness. The cost of reheating and the time involved to apply multiple layers of film decreases the desirability of this method.
It has long been an objective to produce a high energy reflecting coating for the purpose of controlling solar energy transmission through glass. Most desirably, this film should also provide flexibility in color by reflection and transmission. It should be relatively economical and capable of high speed production runs. Dimensions of the glass should not be a limitation on the method of application.